Roof Pitch Calculator
Convert a roof’s rise and run into pitch, angle and slope. Enter the rise and run in any unit (or an angle in degrees) and get the pitch as x : 12, the angle, the percentage slope, the ratio and the multiplier for rafter length and roof area.
Calculate roof pitch
Roof pitch formulas
Pitch (x : 12)
Pitch = rise ÷ run × 12US carpenters describe pitch as inches of rise per 12 inches of run, written 6:12 or 6/12.
Angle
Angle = arctan(rise ÷ run)In the UK, Europe and Asia, roof pitch is usually stated in degrees.
Slope percentage
Slope % = rise ÷ run × 100Rafter / area multiplier
Multiplier = √(1 + (rise ÷ run)²)Multiply the horizontal run by this to get the rafter length, or multiply a roof’s plan (footprint) area by it to get the true sloped area.
Roof pitch to degrees table
| Pitch | Angle | Slope % | Multiplier |
|---|---|---|---|
| 1 : 12 | 4.8° | 8.3% | 1.003 |
| 2 : 12 | 9.5° | 16.7% | 1.014 |
| 3 : 12 | 14.0° | 25.0% | 1.031 |
| 4 : 12 | 18.4° | 33.3% | 1.054 |
| 5 : 12 | 22.6° | 41.7% | 1.083 |
| 6 : 12 | 26.6° | 50.0% | 1.118 |
| 7 : 12 | 30.3° | 58.3% | 1.158 |
| 8 : 12 | 33.7° | 66.7% | 1.202 |
| 9 : 12 | 36.9° | 75.0% | 1.250 |
| 10 : 12 | 39.8° | 83.3% | 1.302 |
| 11 : 12 | 42.5° | 91.7% | 1.357 |
| 12 : 12 | 45.0° | 100% | 1.414 |
| 14 : 12 | 49.4° | 116.7% | 1.537 |
| 16 : 12 | 53.1° | 133.3% | 1.667 |
| 18 : 12 | 56.3° | 150% | 1.803 |
How to measure roof pitch
- From inside the loft: hold a level horizontally against the underside of a rafter, mark 12 in (or 300 mm) along it, and measure straight up from that mark to the rafter. That vertical distance is the rise per 12 (or per 300 mm).
- From drawings: rise is the height from wall plate to ridge; run is half the building span for a symmetrical gable.
- With a phone: place a clinometer or angle app on a rafter or a straight batten resting on the roof and read the angle.
Minimum pitch by roof covering
| Covering | Typical minimum |
|---|---|
| Flat roof membrane / EPDM | about 1–2° (¼ : 12) for drainage |
| Standing seam metal | about 3–14° depending on profile (¼ : 12 to 3 : 12) |
| Asphalt shingles | 2 : 12 with special underlayment, 4 : 12 standard |
| Interlocking concrete tiles | about 12.5–22.5° depending on tile |
| Natural slate | about 20–25° minimum |
| Plain clay tiles | about 35° |
Always check the manufacturer’s minimum pitch for the exact product, as it varies with exposure and lap.
Frequently asked questions
How do I calculate roof pitch?
Divide the rise by the run and multiply by 12 for the x : 12 pitch. A roof that rises 3 m over a 6 m run is 3 ÷ 6 × 12 = 6 : 12, which is 26.6°.
What angle is a 4/12 pitch roof?
18.4 degrees, a 33.3% slope.
What is the most common roof pitch?
For houses in North America, 4 : 12 to 9 : 12 is most common. In the UK, tiled roofs are often 30–45°.
Related calculators
Results are geometric conversions. Follow product and building code requirements for roof design.